In recent years, as a cause of global warming of the earth, the greenhouse effect due to CO2 has been pointed out, and measures against the greenhouse effect is internationally imperative in terms of protection of the earth environment. Generation sources of CO2 extend over every field of human activities that burn fossil fuels, and demands for suppression of emission of CO2 tends to increase. In response to the demands, a method of bringing a flue gas in a boiler in contact with an amine-based CO2 absorbent such as an alkanolamine aqueous solution to remove and recover CO2 in the flue gas, and a method of storing the recovered CO2 without emitting CO2 to the air have been vigorously studied for power generation facilities such as thermal power stations that use a large amount of fossil fuels.
Conventionally, Patent Literature 1 discloses a method of removing CO2 (carbon dioxide) and SOx (sulfur oxide) in a flue gas. This method includes a denitrification process of reducing NOx (nitrogen oxide) contained in a flue gas to perform denitrification treatment, a desulfurization process of bringing SOx contained in the flue gas in contact with calcium carbonate in slurry to perform desulfurization treatment, a CO2 desorption process of bringing the flue gas subjected to the denitrification treatment and the desulfurization treatment in countercurrent contact with an amine-based absorbent (alkanolamine aqueous solution) in an absorber to cause the absorbent to absorb CO2 in the flue gas, and an absorbent regenerating process of obtaining a lean solution by removing CO2 from a rich solution that has absorbed CO2 in a regenerator to put the lean solution back to the absorber again. Then, in this method, to prevent a situation where a deteriorated substance containing a thermally stable salt caused by oxidative degradation of alkanolamine in oxygen in the flue gas and by a reaction of alkanolamine with residual NOx or residual SOx, as well as a solid such as dust contained in the flue gas is accumulated in a system that the absorbent passes through, reclaiming is performed, which includes heating the absorbent in a reclaimer, concentrating a coexisting substance as sludge, and removing the deteriorated substance from the absorbent.